Add initial prototype for the GN meta-buildsystem.

tools/gn/ninja_helper.h

Index: tools/gn/ninja_helper.h
diff --git a/tools/gn/ninja_helper.h b/tools/gn/ninja_helper.h
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index 0000000000000000000000000000000000000000..5bea29ed21421a5caafa685db62cb923e2720bd7
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+++ b/tools/gn/ninja_helper.h
@@ -0,0 +1,71 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef TOOLS_GN_NINJA_HELPER_H_
+#define TOOLS_GN_NINJA_HELPER_H_
+
+#include <iosfwd>
+#include <string>
+
+#include "tools/gn/filesystem_utils.h"
+#include "tools/gn/output_file.h"
+
+class BuildSettings;
+class SourceDir;
+class SourceFile;
+class Target;
+
+// NinjaHelper -----------------------------------------------------------------
+
+class NinjaHelper {
+ public:
+  NinjaHelper(const BuildSettings* build_settings);
+  ~NinjaHelper();
+
+  // Ends in a slash.
+  std::string GetTopleveOutputDir() const;
+
+  // Ends in a slash.
+  std::string GetTargetOutputDir(const Target* target) const;
+
+  // Example: "base/base.ninja". The string version will not be escaped, and
+  // will always have slashes for path separators.
+  OutputFile GetNinjaFileForTarget(const Target* target) const;
+
+  // Returns the name of the root .ninja file for the given toolchain.
+  OutputFile GetNinjaFileForToolchain(const Settings* settings) const;
+
+  // Given a source file relative to the source root, returns the output
+  // filename.
+  OutputFile GetOutputFileForSource(const Target* target,
+                                   const SourceFile& source,
+                                   SourceFileType type) const;
+
+  // Returns the filename produced by the given output.
+  //
+  // Some targets make multiple files (like a .dll and an import library). This
+  // function returns the name of the file other targets should depend on and
+  // link to (so in this example, the import library).
+  OutputFile GetTargetOutputFile(const Target* target) const;
+
+  // Returns the relative directory in either slashes or the system separator
+  // from the ninja directory (e.g. "out/Debug") to the source root (e.g.
+  // "../.."). It has no terminating slash.
+  const std::string& build_to_src_no_last_slash() const {
+    return build_to_src_no_last_slash_;
+  }
+  const std::string& build_to_src_system_no_last_slash() const {
+    return build_to_src_system_no_last_slash_;
+  }
+
+ private:
+  const BuildSettings* build_settings_;
+
+  std::string build_to_src_no_last_slash_;
+  std::string build_to_src_system_no_last_slash_;
+
+  DISALLOW_COPY_AND_ASSIGN(NinjaHelper);
+};
+
+#endif  // TOOLS_GN_NINJA_HELPER_H_